The present invention is directed to an explosive powder charge operated setting tool containing a piston guide forming a piston guide bore for a driving piston. The trailing end of the piston guide has a passageway connected with a cartridge chamber. The passageway leading to the cartridge chamber is enclosed in a support. A housing part laterally encloses the piston guide and is spaced radially outwardly from it. A channel in flow communication with the cartridge chamber is provided between the piston guide and the housing part and the channel is connected to the guide bore through an aperture in the piston guide. A closable passage is located in the housing part and a closable valve arrangement is located in the channel so that a storage space is formed and located in the leading end regions of the channel and of the guide bore.
An explosive powder charge operated setting tool is disclosed in DE-OS 43 13 504 in which a driving piston is driven from a rear position into a front position by propelling gases developed when a propellant charge is ignited. Prior to ignition, the propellant charge is located in a cartridge chamber. The driving piston acts, before reaching its front or driving position, against fastening elements, such as bolts, nails and the like, which are driven into hard receiving materials such as concrete, metal and the like.
A base part located at the trailing end of the piston guide has an axial projection region, facing in the driving direction and formed of a support, an annular surface on the support, and an annular surface of a cartridge chamber guided in the support and located in the same plane. The support chamber is penetrated by a bore connecting the cartridge chamber to the guide bore. The diameter of the base part corresponds to the diameter of the guide bore.
To return the driving piston to its initial position after a driving operation has been completed, so that it is ready for the next driving operation, it must be moved from the front driving position into the rear initial driving position, ready for the next firing operation. The return of the driving piston is achieved, so that when the propellant charge is fired, the channel is still sealed off from the atmosphere. Directly after the driving piston has started to move forwardly through the guide bore, the channel is connected to the guide bore. Accordingly, the propellant gases, after they have acted on the driving piston, arrive in the channel enclosing the leading end of the guide bore. As soon as the leading end region of the channel and the guide bore are filled with the propelling gases, the valve arrangement is closed and a common storage space closed relative to the atmosphere is established. Within the storage space, the propelling gases are compressed by the piston driven forwardly into the front driving position. Next the gases within the channel and the guide bore move the driving piston backwardly, counter to the setting direction, into its rear initial position ready for the next firing operation.
Cartridges, developing a higher driving energy when they are ignited, are used when driving longer fastening elements. As a result, a greater quantity of the propelling gases arrive the storage spaces and are used for driving the driving piston back into its initial position. When fastening elements are driven into soft receiving materials, the driving piston encounters little resistance. Accordingly, the speed of the piston moving in the driving position is greater. Due to the higher speed of the driving piston, a larger quantity of propelling gases is compressed within the storage space. The energy in front of the compressed propellant gases, required for displacing the driving piston back to its initial position, is thus somewhat greater than when driving fastening elements into a hard receiving material.
When the pressure of the propelling gases acts against the driving piston, the piston is moved back into its initial position at such a high rate that it rebounds from the base surface of the piston guide and moves into a position spaced from the base surface. This position of the driving piston has a negative effect on the subsequent driving operations, since the propelling gases produced by the ignited cartridge impact against the piston in a location where the gases are already partially expanded. The driving piston is thus provided with a smaller acceleration in the setting direction. As a result, the fastening element is not driven into the receiving material for the desired depth.